Crude solvent powder removal system and solvent recovery system after production of polyethylene by slurry method

Abstract

The utility model discloses a coarse solvent powder removal system and a solvent recovery system after production of polyethylene by a slurry method. The utility model relates to a powder removal system for a crude solvent after production of polyethylene by a slurry method. The powder removal system comprises a mixing device for alkali liquor and a powder-containing crude solvent, a layering device, a solid-liquid separation device and a waste liquid collection device, wherein a discharge port of the alkali liquor and powder-containing coarse solvent mixing device is connected with a feed port of the layering device. According to the coarse solvent powder removal system, a catalyst is inactivated and powder is removed before solvent refining, the problem that the catalyst is unstable in the system is solved, the problem that a downstream solvent refining system is blocked due to the fact that powder separation is not thorough in the solvent recovery process of a slurry method polyethylene device is solved, the process is simple, the powder removal effect is good, and the cost is low. And the project economy is good.

Description

Technical Field

[0001] This utility model relates to the technical field of crude solvent recovery after polyethylene production by slurry method, and more specifically, to a crude solvent desiccation system and solvent recovery system after polyethylene production by slurry method. Background Technology

[0002] In the production of polyethylene, the slurry polymerization process is an important polymerization technique, particularly suitable for producing high-density polyethylene (HDPE). The key to the slurry process is the fusion of aliphatic hydrocarbon solvent and ethylene, which, under the action of a catalyst, generates a polymer that is suspended in the solvent.

[0003] The polymerized slurry requires a separation process. In existing slurry-based polyethylene production processes, the solvent containing powder is typically filtered to remove dust before being directly fed into a distillation column. However, due to the limited filtration efficiency of the filters, powder separation is incomplete, and impurities from polymer particles or the solvent accumulate within the column, reducing the flow area and causing severe blockage. Furthermore, to ensure optimal filtration, the upstream filters are frequently switched. Additionally, the solvent in existing slurry-based polyethylene production processes contains unreacted catalysts, which can easily destabilize the system. Therefore, the recovery of solvent containing powder in existing slurry-based polyethylene production processes can only be performed intermittently, resulting in high labor and production costs, as well as system instability. Summary of the Invention

[0004] To address the problems in existing technologies, this invention proposes a crude solvent de-dusting system and a solvent recovery system for polyethylene production using the slurry process. The crude solvent de-dusting system of this invention deactivates and removes catalyst dust before solvent refining, eliminating catalyst instability in the system. It also solves the problem of incomplete dust separation during solvent recovery in slurry polyethylene plants, which can lead to blockages in the downstream solvent refining system. This crude solvent de-dusting system features a simple process, excellent dust removal efficiency, and good project economics. Compared to intermittent operation, it improves process stability and ease of operation, significantly reduces filter switching frequency, and decreases manpower input during dust removal, better meeting actual production and processing needs. Furthermore, this invention utilizes the characteristics of powder and solvent for physical dust removal, resulting in high stability and low energy consumption; it is applicable to production at different scales, offering high flexibility.

[0005] One objective of this invention is to provide a crude solvent de-dust removal system for polyethylene production using the slurry process. The system includes a mixing device for alkali solution and powder-containing crude solvent, a stratification device, a solid-liquid separation device, and a waste liquid collection device. The outlet of the mixing device is connected to the inlet of the stratification device. The stratification device includes an upper crude solvent layer, a lower waste alkali solution layer, and a powder-rich solvent layer between them. The outlet of the upper crude solvent layer is connected to a crude solvent extraction pipe. The outlet of the lower waste alkali solution layer is connected to the inlet of the waste liquid collection device. The outlet of the powder-rich solvent layer is connected to the inlet of the solid-liquid separation device.

[0006] As a preferred implementation method,

[0007] The powder-containing crude solvent is the crude solvent containing powder after at least a portion of the polyethylene product has been separated in the slurry process for producing polyethylene; more preferably, the powder-containing crude solvent includes the catalyst after the reaction in the slurry process for producing polyethylene, the solvent used in the slurry process for producing polyethylene, and optionally polyethylene; even more preferably, the content of polyethylene in the powder-containing crude solvent is ≤1%. The powder-containing crude solvent of this invention is the crude solvent containing powder after most of the polyethylene product has been separated in the slurry process for producing polyethylene by centrifugation or other means; this powder-containing crude solvent mainly includes the unreacted catalyst and the solvent used in the slurry process for producing polyethylene.

[0008] In this invention, the catalyst is a titanium-based catalyst, preferably titanium tetrachloride;

[0009] The solvent is an aliphatic hydrocarbon solvent, preferably hexane;

[0010] The alkaline solution is an alkali metal hydroxide, preferably an aqueous solution of sodium hydroxide;

[0011] The concentration of the alkaline solution is 5-10 wt%; it can be determined according to the OH content of the alkaline solution. - When adding alkaline solution, the molar ratio of unreacted catalyst acidic ions (such as Cl-) in the crude solvent containing powder is 1:1.

[0012] As a preferred implementation method,

[0013] The mixing device for the alkaline solution and the crude solvent containing powder is a tank equipped with a mixing device; more preferably, it is a conventional tank equipped with a stirring device.

[0014] As a preferred implementation method,

[0015] The mixing device for alkali solution and powdered crude solvent is equipped with alkali solution feed pipe and powdered crude solvent feed pipe respectively.

[0016] As a preferred implementation method,

[0017] The mixing apparatus for the alkaline solution and the crude solvent containing powder is also equipped with an interface meter to measure the liquid level within the apparatus. The interface meter is a commonly used interface meter.

[0018] As a preferred implementation method,

[0019] The stratification device is a tank, and any existing ordinary tank that can meet the material stratification requirements is acceptable.

[0020] As a preferred implementation method,

[0021] The feed inlet of the layering device is located in the upper middle part of the layering device; preferably in the middle of the layering device.

[0022] As a preferred implementation method,

[0023] The coarse solvent layer overflows into the coarse solvent extraction pipe through the coarse solvent layer outlet. In this invention, the coarse solvent layer is located above the stratification device. There are no special requirements for the outlet position of the coarse solvent layer, as long as it can overflow the coarse solvent without overflowing the rich powder solvent layer. This position can be estimated by parameters such as the expected upstream feed rate, powder content, residence time, powder density, or tank diameter. Alternatively, the approximate outlet position of the coarse solvent layer can be simulated experimentally.

[0024] As a preferred implementation method,

[0025] The outlet of the rich powder solvent layer is connected to the inlet of the solid-liquid separation device through a rich powder solvent conveying pipe.

[0026] As a preferred implementation method,

[0027] The outlet of the waste alkali liquid layer is connected to the inlet of the waste liquid collection device through a waste alkali liquid conveying pipe.

[0028] As a preferred implementation method,

[0029] The outlet of the rich powder solvent layer is located at the bottom of the rich powder solvent layer; so that the rich powder solvent layer flows by gravity through the outlet of the rich powder solvent layer to the rich powder solvent conveying pipe.

[0030] As a preferred implementation method,

[0031] The outlet of the waste alkali liquid layer is located at the bottom of the stratification device; the waste alkali liquid layer flows through the outlet of the waste alkali liquid layer to the waste alkali liquid conveying pipe by gravity.

[0032] As a preferred implementation method,

[0033] The crude solvent extraction pipeline is equipped with a powder filter; the powder filter can filter the powder in the crude solvent extraction pipeline to ensure that the powder content of the solvent in the downstream crude solvent distillation system does not exceed the standard under abnormal operating conditions.

[0034] The rich powder solvent delivery pipe is also equipped with a sight glass; through the sight glass, it is possible to effectively observe whether the rich powder solvent layer has been completely discharged, making the operation convenient and quick.

[0035] The waste alkali solution conveying pipe is also equipped with an online pH analyzer; the online pH analyzer is used to determine the consumption of added alkali solution. If the pH is less than 9, fresh alkali solution can be added to the mixing device containing alkali solution and powdered crude solvent.

[0036] The layering device is also equipped with an interface meter II for measuring the height of the waste alkali liquid layer. By measuring the height of the waste alkali liquid layer with the interface meter II, the installation position of the sight glass can be better determined. The sight glass is generally installed at the top of the waste alkali liquid layer and at the bottom of the powder-rich solvent layer.

[0037] As a preferred implementation method,

[0038] The solid-liquid separation device is a device capable of heating and evaporating solvent; the solvent outlet pipe of the solid-liquid separation device is connected to the inlet of the crude solvent extraction pipe; the powder-rich phase outlet pipe of the solid-liquid separation device is connected to the inlet of the waste liquid collection device.

[0039] As a preferred implementation method,

[0040] The solvent outlet pipe of the solid-liquid separation device is connected to the crude solvent extraction pipe after being condensed by a condenser. Through the heating and evaporation action of the solid-liquid separation device, the solvent in the powder-rich solvent layer is evaporated and sent to the crude solvent extraction pipe. The remaining material in the solid-liquid separation device is mainly powder, which is discharged to the waste liquid collection device.

[0041] The working process of the coarse solvent de-dust removal system after polyethylene production by the slurry method of this invention is as follows:

[0042] First, alkali solution and powdered crude solvent are introduced into a mixing device. The powdered crude solvent mainly includes unreacted catalyst from the slurry method of polyethylene production and the solvent used in the slurry method of polyethylene production. By mixing with the alkali solution, the alkali solution quenches the unreacted catalyst from the polyethylene production process, eliminating the instability of the catalyst in the system. Then, the quenched powdered material enters a stratification device. Due to the differences in density and solubility of the crude solvent, powder, and alkali solution, it separates into an upper crude solvent layer, a lower waste alkali solution layer, and a powder-rich solvent layer in between. In the device, as material is continuously fed into the stratification unit, the liquid level rises, and the upper coarse solvent layer overflows automatically first. After overflow, the valves of the coarse solvent extraction pipe and the feed valve of the stratification unit are closed. Next, the middle rich powder solvent layer is discharged, which can be a bagless gravity flow. When the stratification unit discharges the rich powder solvent layer, the valve of the rich powder solvent delivery pipe is opened, and the discharge status of the coarse solvent layer is judged through the sight glass on the rich powder solvent delivery pipe. When the liquid changes from clear to turbid and then back to clear as observed through the sight glass, it is determined that the powder has been completely discharged, and the valve of the rich powder solvent delivery pipe is closed. Finally, the waste alkali liquid layer flows to the waste liquid collection device by gravity. The valve of the waste alkali liquid delivery pipe is opened, and the waste alkali liquid flows to the waste liquid collection device by gravity. Waste alkali liquid is discharged by observing the interface gauge or by scheduled discharge for 3 minutes per shift.

[0043] The material extracted from the rich solvent layer enters the solid-liquid separation device. Through the heating and evaporation action of the solid-liquid separation device, the solvent in the rich solvent layer is evaporated and sent to the crude solvent extraction pipeline. The solid-liquid separation device mainly contains powder, which is discharged to the waste liquid collection device by gravity.

[0044] The waste liquid collection device contains trace amounts of powder; there is a baffle between the inlet and outlet of the waste liquid collection device, and the trace amounts of powder float on the surface of the waste liquid collection device after accumulating for a long time, which can be skimmed off by a long-handled sieve; the wastewater is discharged into the production wastewater pond through a sloping pipe.

[0045] The second objective of this invention is to provide a crude solvent recovery system for polyethylene production using the slurry process. This system includes a crude solvent dust removal system and a crude solvent distillation system, as described in the first objective of this invention. The outlet of the crude solvent dust removal system is connected to the inlet of the crude solvent distillation system. The crude solvent distillation system of this invention can utilize existing solvent distillation systems. The solvent recovered through the distillation system can then be reused as a solvent in the slurry process for polyethylene production.

[0046] The endpoints and any values ​​of the ranges disclosed in this utility model are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0047] Beneficial effects:

[0048] (1) This utility model deactivates and removes the powder from the catalyst before solvent refining, which eliminates the instability of the catalyst in the system and solves the problem of incomplete powder separation leading to blockage of the downstream solvent refining system during the solvent recovery process of the slurry polyethylene plant. The process is simple, the powder removal effect is good, and the project is economical.

[0049] (2) The continuous catalyst deactivation and dust removal method developed in this utility model is simple to operate, easy to observe, significantly reduces manpower input, and greatly improves the safety factor, which is of great significance to the industrialization and commercialization of polyethylene materials. Compared with intermittent operation, the process stability and ease of operation are improved, the manpower input in the dust removal process is reduced, and it is more in line with the actual production and processing needs.

[0050] (3) This utility model utilizes the properties of powder and solvent for physical powder removal, which has high stability and low energy consumption. Moreover, the process of this utility model is applicable to production at different scales, the equipment is simple, there is no scale bottleneck, it is highly flexible and widely applicable, which is of great significance to the large-scale production of polyethylene materials. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the coarse solvent de-dust removal system after polyethylene production using the slurry method of this invention.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1-A mixing device for alkaline solution and crude solvent containing powder;

[0054] 2-Layered device;

[0055] 3-Solid-liquid separation device;

[0056] 4- Waste liquid collection device;

[0057] 101-Alkali feed pipe;

[0058] 102 - Feed pipe containing powdered crude solvent;

[0059] 103 - Alkali-washed solvent-containing conveying pipe;

[0060] 104-Interface Design 1;

[0061] 201 - Crude solvent extraction pipeline;

[0062] 202-Rich Powder Solvent Delivery Pipe;

[0063] 203 - Waste Alkali Solution Conveying Pipe;

[0064] 204 Powder Filter;

[0065] 205-Sight Mirror;

[0066] 206 - Online pH Analyzer;

[0067] 207-Interface Design II;

[0068] 301 - Solvent outlet pipe of solid-liquid separation device;

[0069] 302 - Powder-rich phase discharge pipe of solid-liquid separation device;

[0070] 303 - Condenser;

[0071] 304 - Air-operated regulating valve. Detailed Implementation

[0072] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0073] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this utility model will not describe the various possible combinations separately.

[0074] Furthermore, various different embodiments of this utility model can be combined arbitrarily, as long as they do not violate the spirit of this utility model. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of this utility model.

[0075] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0076] Example 1

[0077] like Figure 1 As shown, this utility model discloses a crude solvent de-dust removal system for polyethylene production using the slurry method. The system includes a mixing device 1 for alkali solution and powder-containing crude solvent, a stratification device 2, a solid-liquid separation device 3, and a waste liquid collection device 4. The outlet of the mixing device 1 is connected to the inlet of the stratification device 2. The stratification device 2 includes an upper crude solvent layer, a lower waste alkali solution layer, and a powder-rich solvent layer between them. The outlet of the upper crude solvent layer is connected to a crude solvent extraction pipe 201. The outlet of the lower waste alkali solution layer is connected to the inlet of the waste liquid collection device 4. The outlet of the powder-rich solvent layer is connected to the inlet of the solid-liquid separation device 3.

[0078] In a preferred embodiment, the powder-containing crude solvent is the powder-containing crude solvent after at least a portion of the polyethylene product has been separated in the slurry process for producing polyethylene; more preferably, the powder-containing crude solvent includes the catalyst after the reaction in the slurry process for producing polyethylene, the solvent used in the slurry process for producing polyethylene, and optionally polyethylene; even more preferably, the content of polyethylene in the powder-containing crude solvent is ≤1%. The powder-containing crude solvent of this invention is the powder-containing crude solvent after most of the polyethylene product has been separated by centrifugation or other methods in the slurry process for producing polyethylene; the powder-containing crude solvent of this invention mainly includes the unreacted catalyst and the solvent used in the slurry process for producing polyethylene. In a preferred embodiment, the mixing device 1 for the alkali solution and the powder-containing crude solvent is a conventional tank with a mixing device; more preferably, it is a conventional tank with a stirring device.

[0079] As a preferred implementation method,

[0080] The mixing device 1 for alkaline solution and powdered crude solvent is provided with an alkaline solution feed pipe 101 and a powdered crude solvent feed pipe 102.

[0081] As a preferred implementation method,

[0082] The outlet of the lower waste alkali liquid layer is connected to the inlet of the waste liquid collection device 4 through the waste alkali liquid conveying pipe 103.

[0083] As a preferred implementation method,

[0084] The mixing device 1 for alkaline solution and crude solvent containing powder is also equipped with an interface meter 104 for measuring the liquid level in the device. The interface meter 104 is a commonly used interface meter.

[0085] As a preferred implementation method,

[0086] The layering device 2 is a regular tank.

[0087] As a preferred implementation method,

[0088] The feed inlet of the layering device 2 is located in the upper middle part of the layering device 2; preferably in the middle part of the layering device 2.

[0089] As a preferred implementation method,

[0090] The coarse solvent layer overflows into the coarse solvent extraction pipe 201 through the coarse solvent layer outlet. In this utility model, the coarse solvent layer is located above the layering device 2. There are no special requirements for the location of the coarse solvent layer outlet, as long as it can overflow the coarse solvent without overflowing the rich powder solvent layer.

[0091] As a preferred implementation method,

[0092] The outlet of the rich solvent layer is connected to the inlet of the solid-liquid separation device 3 through the rich solvent conveying pipe 202.

[0093] As a preferred implementation method,

[0094] The outlet of the waste alkali liquid layer is connected to the inlet of the waste liquid collection device 4 through the waste alkali liquid conveying pipe 203.

[0095] As a preferred implementation method,

[0096] The outlet of the rich powder solvent layer is located at the bottom of the rich powder solvent layer; so that the rich powder solvent layer flows by gravity through the outlet of the rich powder solvent layer to the rich powder solvent conveying pipe 202.

[0097] As a preferred implementation method,

[0098] The outlet of the waste alkali liquid layer is located at the bottom of the layering device 2; the waste alkali liquid layer flows through the outlet of the waste alkali liquid layer to the waste alkali liquid conveying pipe 203 by gravity.

[0099] As a preferred implementation method,

[0100] The crude solvent extraction pipeline 201 is equipped with a powder filter 204; the powder filter 204 can filter the powder in the crude solvent extraction pipeline to ensure that the powder content of the solvent in the downstream crude solvent distillation system does not exceed the standard under abnormal operating conditions.

[0101] The rich powder solvent delivery pipe 202 is also equipped with a sight glass 205; through the sight glass 205, it is possible to effectively observe whether the rich powder solvent layer has been completely discharged, making the operation convenient and quick.

[0102] The waste alkali liquid conveying pipe 203 is also equipped with an online pH analyzer 206; the online pH analyzer 206 is used to determine the consumption of added alkali liquid. If the pH is <9, fresh alkali liquid can be added to the mixing device containing alkali liquid and powdered crude solvent.

[0103] The layering device 2 is also equipped with an interface meter 207 for measuring the height of the waste alkali liquid layer. The installation position of the sight glass 205 can be better determined by the measurement of the interface meter 207. The sight glass 205 is generally installed at the top of the waste alkali liquid layer and at the bottom of the powder-rich solvent layer.

[0104] As a preferred implementation method,

[0105] The solid-liquid separation device 3 is a device capable of heating and evaporating solvent; the solvent outlet pipe 301 of the solid-liquid separation device 3 is connected to the inlet of the crude solvent collection pipe 201; the powder-rich phase outlet pipe 302 of the solid-liquid separation device 3 is connected to the inlet of the waste liquid collection device 4.

[0106] As a preferred implementation method,

[0107] The solvent outlet pipe 301 of the solid-liquid separation device 3 is condensed by the condenser 303 and then connected to the crude solvent outlet pipe 201. Through the heating and evaporation of steam in the solid-liquid separation device 3, and with a steam-opening regulating valve 304 on the steam, the solvent in the rich powder solvent layer is evaporated and sent to the crude solvent outlet pipe 201. The remaining material in the solid-liquid separation device 3 is mainly powder, which is discharged into the waste liquid collection device 4.

[0108] The working process of the coarse solvent de-dust removal system after polyethylene production by the slurry method of this invention is as follows:

[0109] First, alkali solution and powdered crude solvent are introduced into a mixing device 1. The powdered crude solvent mainly includes unreacted catalyst from the slurry method of polyethylene production and the solvent used in the slurry method of polyethylene production. Through mixing with the alkali solution, the alkali solution quenches the unreacted catalyst from the polyethylene production process. Then, the quenched powdered material enters a stratification device 2. Due to the differences in density and solubility of the crude solvent, powder, and alkali solution, it separates into an upper crude solvent layer, a lower waste alkali solution layer, and a powder-rich solvent layer in between. In the stratification device 2, as material is continuously fed in... The liquid level in the stratification device 2 rises, and the upper coarse solvent layer overflows first. After overflow, the valve of the coarse solvent outlet pipe 201 and the feed valve of the stratification device 2 are closed. Next, the middle rich powder solvent layer is discharged, which can be a bagless gravity flow. When the stratification device 2 discharges the rich powder solvent layer, the valve of the rich powder solvent conveying pipe 202 is opened, and the discharge status of the coarse solvent layer is judged by the sight glass 205 on the rich powder solvent conveying pipe 202. When the liquid changes from clear to turbid and then back to clear as observed through the sight glass 205, it is judged that the powder has been completely discharged, and the valve of the rich powder solvent conveying pipe 202 is closed. Finally, the waste alkali liquid layer flows to the waste liquid collection device by gravity. The valve of the waste alkali liquid conveying pipe 203 is opened, and the waste alkali liquid flows to the waste liquid collection device by gravity. The waste alkali liquid is discharged by observing the interface of interface gauge 207 or by a fixed discharge of 3 minutes per shift.

[0110] The material extracted from the rich solvent layer enters the solid-liquid separation device 3. Through the heating and evaporation of the solid-liquid separation device 3 by steam, the solvent in the rich solvent layer is evaporated and sent to the crude solvent extraction pipe 201. The remaining material in the solid-liquid separation device 3 is mainly powder, which is discharged to the waste liquid collection device 4 by gravity.

[0111] The waste liquid collection device 4 contains trace amounts of powder; there is a baffle between the inlet and outlet of the waste liquid collection device 4, and the trace amounts of powder float on the surface of the waste liquid collection device 4 after accumulating for a long time, and can be skimmed off by a long-handled sieve; the wastewater is discharged to the production wastewater pond through a sloping pipe.

[0112] Example 2

[0113] This invention also provides a crude solvent recovery system for polyethylene production using the slurry process. The solvent recovery system includes a crude solvent dust removal system and a crude solvent distillation system as described in any of the embodiments in Example 1. The outlet of the crude solvent collection pipe of the crude solvent dust removal system is connected to the inlet of the crude solvent distillation system. The crude solvent distillation system of this invention can utilize existing commonly used solvent distillation systems. The solvent recovered through the solvent distillation system can be further reused as a solvent in the slurry process for polyethylene production.

[0114] Existing solvent de-dust removal processes using filters can only operate intermittently, requiring filter replacement at least once a day per shift. In contrast, the crude solvent de-dust removal system of this invention can operate continuously for at least a week. This invention develops a continuous control method for controlling the discharge of waste alkaline solution at the layered interface height, enabling industrial-scale continuous production, ensuring low solvent powder content, significantly improving the column blockage problem in the crude solvent distillation system (solvent refining system), and greatly enhancing economic efficiency.

[0115] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present invention without departing from the spirit and scope of the present invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0116] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0117] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application’s filing, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0118] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A system for removing fines from a crude solvent after a slurry process for producing polyethylene, characterized by: The system comprises a mixing device of lye and crude solvent containing powder, a layering device, a solid-liquid separation device, and a waste liquid collecting device; the outlet of the mixing device is connected with the inlet of the layering device; the layering device comprises a crude solvent layer in the upper layer, a waste lye layer in the lower layer, and a rich powder solvent layer between the two layers; the outlet of the crude solvent layer is connected with a crude solvent outlet pipeline; the outlet of the waste lye layer is connected with the inlet of the waste liquid collecting device; and the outlet of the rich powder solvent layer is connected with the inlet of the solid-liquid separation device.

2. The system according to claim 1, wherein the crude solvent containing powder is the crude solvent containing powder after separating at least part of the polyethylene product produced by the slurry method.

3. The system according to claim 1, wherein the mixing device of lye and crude solvent containing powder is a tank with a mixing device; and / or the mixing device is respectively provided with a lye feeding pipeline and a crude solvent containing powder feeding pipeline; and / or the mixing device is further provided with an interface meter for measuring the liquid level in the device.

4. The system according to claim 1, wherein the layering device is a tank; and / or the inlet of the layering device is located in the upper middle part of the layering device.

5. The system according to claim 1, wherein the crude solvent layer overflows to the crude solvent outlet pipeline through the outlet of the crude solvent layer; and / or the outlet of the rich powder solvent layer is connected with the inlet of the solid-liquid separation device through a rich powder solvent conveying pipeline; and / or the outlet of the waste lye layer is connected with the inlet of the waste liquid collecting device through a waste lye conveying pipeline.

6. The system according to claim 1, wherein the outlet of the rich powder solvent layer is located at the bottom of the rich powder solvent layer; and / or the outlet of the waste lye layer is located at the bottom of the layering device.

7. The system according to claim 5, wherein the crude solvent outlet pipeline is provided with a powder filter; and / or the rich powder solvent conveying pipeline is further provided with a sight glass; and / or the waste lye conveying pipeline is further provided with an on-line PH analyzer; and / or the layering device is further provided with an interface meter II for measuring the height of the waste lye layer.

8. The system according to claim 1, wherein the solid-liquid separation device is a device capable of heating and evaporating solvent; the solvent outlet pipeline of the solid-liquid separation device is connected with the inlet of the crude solvent outlet pipeline; and the powder-rich phase outlet pipeline of the solid-liquid separation device is connected with the inlet of the waste liquid collecting device.

9. The system according to claim 8, wherein the solvent outlet pipeline of the solid-liquid separation device is connected with the crude solvent outlet pipeline after being condensed by a condenser. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 10. A crude solvent recovery system for a slurry process for producing polyethylene, characterized in that: the solvent recovery system comprises the crude solvent de-dusting system and the crude solvent rectification system for the slurry process for producing polyethylene according to any one of claims 1 to 9; and the outlet of the crude solvent outlet pipeline of the crude solvent de-dusting system is connected to the inlet of the crude solvent rectification system.

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